Clutched damper for a belt tensioner

ABSTRACT

A tensioner is disclosed that achieves asymmetric damping in part by using a ramp-ramp assembly. The tensioner comprises a tensioner axle defining a pivot axis, an arm mounted on the tensioner axle so as to permit the arm to pivot about the pivot axis, a first tensioner component having first ramp features, a second tensioner component having second ramp features, and a ramp bushing having an upper ramp surface and a lower ramp surface. The first tensioner component is engaged to the arm for rotation therewith and the second tensioner component is coupled to the tensioner axle. The ramp bushing is disposed between the first tensioner component and the second tensioner component such that the upper ramp surface seats within the first ramp features and the lower ramp surface seats within the second ramp features.

TECHNICAL FIELD

The present invention relates generally to tensioners and moreparticularly to an asymmetrically damped tensioner utilizing a ramp-rampclutch assembly operatively engaged with the tensioner arm.

BACKGROUND

It is common for a belt tensioner to have a means to dampen movement ofthe tensioner arm caused by belt tension fluctuation. The requiredmagnitude of this damping depends on many drive factors includinggeometry, accessory loads, accessory inertia, engine duty cycle andothers. For instance, drive systems that have higher torsional input orcertain transient dynamic conditions may require higher damping tosufficiently control tensioner movement. Although higher damping is veryeffective at controlling arm movement, it can also be detrimental toother critical tensioner functions (e.g. slow or no response to slackbelt conditions). In addition, variation or change in damping that occuras a result of manufacturing variation, operating temperature andcomponent break-in or wear can also cause the tensioner to beunresponsive.

Timing belt systems have benefited from the use of asymmetric damping toaddress this problem. An asymmetrically damped tensioner providesdamping when additional belt tension is encountered but is free torespond to slack belt conditions. Although asymmetric functionality maynot be required for all other front end accessory drive tensioners, thepotential for increased service life, solving other transient dynamicsystem problems including belt slip during a 1-2 gear shift, or simplymaking the tensioner less sensitive to damping variation make it adesirable design option.

One current solution to this problem uses a viscous linear dampermechanism, such as a shock absorber, attached to a pivoting arm.Asymmetric damping is achieved through, for example, check valves anddifferent orifice sizes in the shock absorber. This solution, however,tends to be expensive and requires more packaging space than aconventional tensioner. Other solutions use wedges that increase damperfriction during wind-up or spring loaded self-energizing brake shoeelements. These designs, however, tend to be complex with many smallparts to assemble.

One-way clutch mechanisms have been proposed, for example in U.S. Pat.Nos. 4,583,962 and 6,422,962, for timing belt tensioners for the purposeof preventing or limiting back travel to prevent tooth jump. These“ratcheting” tensioners, however, lack the ability to relieve belttension sufficiently when not required. Other timing belt tensionerproposals including, for example, U.S. Pat. Nos. 4,832,665 and6,375,588, use a one-way device coupled to a viscous damper. Althoughthese devices offer good functionality, retention of the viscous fluidthroughout the service life can be difficult. Yet another designdisclosed in U.S. Patent App. Publication 2003/0008739 uses frictiongenerated by the clamping action of a wrap spring clutch to providedamping.

The aforementioned tensioner designs are not ideal. Accordingly, a newtensioner design is desired.

SUMMARY

One aspect of the invention is a belt tensioner including a ramp-rampassembly. In one embodiment, the tensioner includes a tensioner axledefining a pivot axis, an arm mounted on the tensioner axle so as topermit the arm to pivot about the pivot axis, a first tensionercomponent having first ramp features, a second tensioner componenthaving second ramp features, and a ramp bushing having an upper rampsurface and a lower ramp surface. The first tensioner component isengaged to the arm for rotation therewith and the second tensionercomponent is coupled to the tensioner axle. The ramp bushing is disposedbetween the first tensioner component and the second tensioner componentsuch that the upper ramp surface seats within the first ramp featuresand the lower ramp surface seats within the second ramp features.

In another embodiment, the tensioner includes a tensioner axle defininga pivot axis, an arm pivotable about the pivot axis in a first directionand a second direction, a spring case pivotable about the pivot axis andengaged to the arm for rotation therewith, and an end cap coupled to thespring case. The spring case includes first ramp features and the endcap includes second ramp features. The tensioner includes a ramp bushingdisposed between the spring case and the end cap. The ramp bushing has aspring case side having a first ramp surface that seats within the firstramp features and an end cap side having a second ramp surface thatseats within the second ramp features. The tensioner also includes atorsional spring disposed within the spring case. The torsional springis coupled to the arm such that the spring winds up when the arm pivotsabout the pivot axis in a first direction and unwinds when the armpivots about the pivot axis in a second direction to provide asymmetricdampening.

In another embodiment, the tensioner includes a tensioner axle defininga pivot axis, an arm mounted on the tensioner axle so as to permit thearm to pivot about the pivot axis, and a clutch assembly mounted atleast partially to the tensioner axle and coupled to the arm. The clutchassembly comprises a first tensioner component having first rampfeatures, a second tensioner component having second ramp features, aflatwire spring having a first end and a second end, and a damperbushing coupled to the first tensioner component. The first tensionercomponent is engaged with the arm to rotate therewith and the secondtensioner component is coupled to the tensioner axle. The first end ofthe flatwire spring is coupled to the first tensioner component and thedamper bushing is positioned for frictional contact with the arm suchthat when the arm experiences wind-up the spring case rotates with thearm and moves up the second ramp features of the second tensionercomponent which pushes the damper bushing against the arm for frictionaldamping.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is an exploded perspective view of an embodiment of a tensionerincluding a ramp-ramp assembly.

FIG. 2 is a side, cross-sectional view of the assembled tensioner ofFIG. 1.

FIG. 3 is a plan view, in section, along line 3-3 in FIG. 2.

FIG. 4 is a rear cut away, perspective view of the ramp bushing in FIG.1.

FIGS. 5A-5C are schematic views depicting the interface between thefirst tensioner component, a ramp bushing, and a second tensionercomponent according to one embodiment.

FIG. 6 is a side, cross-sectional view of a second embodiment of atensioner having a ramp-ramp assembly.

FIGS. 7A and 7B are exploded perspective views of the ramp-ramp assemblyof the tensioner of FIG. 6.

DETAILED DESCRIPTION

The tensioner disclosed herein provides an asymmetric frictional damperthat will activate during a wind-up (i.e. untensioning) to mitigate thedeleterious effects of wind-up. Wind-up results when increasing belttension causes the belt to lift the tensioner arm in a direction awayfrom the belt. To mitigate the negative effects of wind up, it isdesirable to have a frictional damper on the tensioner arm that willresist the lifting of the tensioner arm from the belt without adverselyeffecting movement of the tensioner arm toward the belt. This kind offrictional damping operating to resist lifting of the tensioner arm onlyis generally known as asymmetric damping.

The tensioner disclosed herein achieves asymmetric damping in part byusing a brake element, which may be referred to herein as a ramp-rampassembly. The ramp-ramp assembly may be comprised of at least twotensioner components having ramp features that interface with eachother. The ramp-ramp assembly may also include a ramp bushing.

At least one of the tensioner components having a ramp feature ismovable such that one-way or asymmetric frictional damping is providedto oppose the movement of the tensioner arm when the arm begins to moveaway from the belt. The movable component enables the device to applyprogressively more frictional damping to counteract the lifting of thetensioner arm from the belt the further the tensioner arm is lifted. Theability to progressively increase frictional damping relative todisplacement of the tensioner arm enables the device to provide greaterfrictional damping in response to greater displacements of the tensionerarm away from the belt. This creates a feedback loop to combat thedeleterious effects of wind-up; the more the tensioner arm is drivenaway from the tensioned belt, the more frictional damping is applied tostop the wind-up. The asymmetric damping may be tailored such that itwill not restrict all movement in the wind-up direction therebyproviding additional compliance that is advantageous for someapplications. Since the damping is asymmetric in nature by design, asthe tensioner returns to normal operation—whereby the tensioner armreturns back to a tensioning contact with the belt—the amount offrictional damping applied to the motion of the device in the tensioningdirection is less than that applied during wind-up.

Referring now to the embodiment shown in FIGS. 1 and 2, the tensioner 10includes an arm 1, a tensioner axle 12 defining a pivot axis 11, a firsttensioner component 5 having a first set of ramp features 9, a secondtensioner component 4 having a second set of ramp features 6, and a rampbushing 3. The tensioner axle 12 is substantially coaxial with the pivotaxis 11 and the arm 1 is mounted on the tensioner axle 12 so as topermit the arm 1 to pivot about the pivot axis 11.

The first tensioner component 5 may be coupled to the arm 1 to pivottherewith. Additionally, the first tensioner component 5 may house atorsional spring 2, and thus may be a spring case. Alternately, oneskilled in the art will appreciate that the first tensioner componentmay be any other component of the tensioner that has a first set of rampfeatures and is coupled to the arm 1 so that the component pivots whenthe arm 1 pivots about the pivot axis 11. Referring to the embodiment ofFIG. 1, the second tensioner component 4 may be coupled to the tensioneraxle 12, and may be an end cap that at least partially closes thetensioner. Alternately, one skilled in the art will appreciate that thesecond tensioner component 4 is not limited to the end cap, but may beany other component of the tensioner having a second set of rampfeatures. The ramp bushing 3, if present, may be disposed between thefirst tensioner component 5 and the second tensioner component 4. Theramp bushing 3 includes an upper ramp surface 7 and a lower ramp surface8. The upper ramp surface 7 seats within the first set of ramp features9 on the first tensioner component 5. The lower ramp surface 8 seatswithin the second set of ramp features 6 on the second tensionercomponent 4. The use of the ramp bushing 3 is advantageous in that itprovides a lower coefficient of friction between the ramp features 6 and9 and can prevent the ramp features 6 and 9 from wearing grooves intoone another. The bushing also provides a more stable coefficient offriction between the two surfaces thereby maintaining a more consistentasymmetry ratio throughout the life of the tensioner.

The arm 1 may be mounted over the tensioner axle 12 so as to pivot aboutaxis 11. The distal end of the arm 1, opposite the pivot axis 11, may beconfigured to receive a belt-contacting pulley 22. The pulley may bemounted on the distal end of the tensioner arm 1 by a bolt 23 or otherfastener known to one of skill in the art and may include a cover 24.The torsional spring 2 exerts a force on the arm 1 to bias the pulley 22in the direction A to tension a belt. Wind-up of the tensioner in theopposite direction B is resisted by bias of the torsional spring 2augmented by the asymmetric frictional damping mechanism. The asymmetricfrictional damping does not substantially impede movement of the arm indirection A while substantially limiting movement of the arm indirection B through the application of progressively greater frictionaldamping as the tensioner arm is further displaced.

The second tensioner component 4, which may be an end cap, providesmeans for affixing the tensioner to an engine or device. Multiplemethods of affixing a tensioner relative to a belt to be tensioned arewell known in the art including, but not limited to, the use of welds,bolts, screws, and locking structures. Alternatively, the tensioner maybe mounted to the engine or device on the opposite side of the tensionerarm from the end cap using an axle passing through the tensioner alongthe pivot axis. Regardless of the method of mounting the device to theengine or device, the approaches taken to create the asymmetric forcesto combat wind-up are substantially unchanged.

Referring to the embodiment shown in FIGS. 1 and 2, the tensioner axle12 provides a bearing surface that enables both rotational andtranslational movement of components in the tensioner 10. Translationalmotion is substantially parallel to and along the pivot axis 11. Theramp features 6 of the second tensioner component 4 are formed on itsinterior surface facing the tensioner arm and are arrayed substantiallycircumferentially around the tensioner axle 12.

The second tensioner component 4, including the ramp features 6,tensioner axle 12 and other elements can be fabricated as a single unitusing a variety of techniques including forging, casting, die-casting,sintering, or machining or fabricated in different components and thenjoined together using a variety of methods such as sintering, welding,bonding, bolting, and even interference fits. In an alternativeembodiment, for example, the ramp features 6 can be formed as a separateplate that may be integrated with the second tensioner component 4. Byfabricating the individual elements as separate components it may beeasier to provide specific surface or heat treatments or coatings to acomponent separate from the entire integrated unit.

Still referring to the embodiment in FIG. 1, the tensioner 10 includes aramp bushing 3 having an upper ramp surface 7 and a lower ramp surface 8opposite the first side. The ramp bushing 3 is both rotatable about andtranslatable along the pivot axis 11 within the tensioner 10. The rampbushing 3 interfaces with the second tensioner component 4 via the lowerramp surface 8 of the ramp bushing 3 which seats within the rampfeatures 6 of the second tensioner component 4. The lower ramp surface 8has the opposite feature profile of the upper ramp surface 7 whichinterfaces with the ramp features 9 located on the tensioner component5.

The tensioner component 5 houses a torsional spring 2 or othercomponents of the tensioner. The torsional spring 2 may be a coilspring, a round wire spring, a flatwire spring, or other spring typesknown to one of skill in the art. As shown in FIGS. 1 and 3, an outertang 14 of torsional spring 2 engages the tensioner component 5 at afirst spring engagement point 17 a. The first spring engagement point 17a may be sized to suitably accept both the spring tang 14 and a plug 26,which may be deformable. An inner tang 13 of spring 2 engages thetensioner arm 1 at a second spring engagement point 17 b along the armarbor 16.

The spring 2 provides a torsional force to bias the tensioner arm 1 intothe belt being tensioned to tension the belt during normal operations.The spring 2 also provides an opposing torsional force to urge the rampbushing 3 to rotate in the opposite direction from the tensioner arm 1.The force imposed on the first tensioner component 5 by the spring 2causes the first tensioner component 5 to move up the ramp features ofeither the ramp bushing 3 or the second tensioner component 4 anequilibrium state is reached.

If the torsional spring 2 is a flatwire spring, spring tape 21 may bepositioned between the coils of the flatwire spring as shown in FIGS.1-3. The spring tape 21 may be coiled in a juxtaposed position with theflatwire spring 2, such that the spring tape 21 is between the coils ofthe flatwire spring and may also be between the flatwire spring 2 andthe interior walls of the tensioner component that houses the spring.The use of spring tape 21 reduces frictional wear of the spring or othernegative affects of friction such that spring collapse is reduced.

The tensioner 10, as shown in FIGS. 1 and 2, may also include a damperbushing 18, and a pivot bushing 15. The pivot bushing 15 is asubstantially cylindrical structure that is inserted into the arm arbor16 of the tensioner arm 1 that is substantially aligned with the pivotaxis 11. The pivot bushing 15 provides a bearing surface for therotation and translation of elements of the tensioner 10 along and aboutthe pivot axis 11. The damper bushing 18 may act as a cover for thetensioner component 5 to dampen sound and/or vibration and to containthe spring 2 within the tensioner component 5 when it houses the spring2. The tensioner 10 may also include an arm plate bushing 19 and an armplate 20 connected to the tensioner arm 1. An end nut, bolt, or fastenermay hold the tensioner 10 together along the pivot axis when assembledas shown in FIG. 2. The end nut bolt or fastener may also attach oraffix the tensioner 10 to an engine or device as discussed above.

The tensioner 10, as shown in FIG. 1, may include a tab and notch forassembling the second tensioner component 4 and the first tensionercomponent 5. The second tensioner component 4, as shown in thisembodiment, includes a notch 27 in its periphery and the first tensionercomponent 5 includes a tab 28 that extends toward the second tensionercomponent 4 and is receivable in notch 27. The notch 27 is larger thantab 28 such that the notch 27 does not act as a stop to inhibitrotational motion of the arm during wind-up. In other words, notch 27 islarge enough to provide the amount of rotational motion of the tensionerarm 1 pre-selected to reach the maximum amount of frictional damping thetensioner is to provide. Alternately, however, the notch 27 may act as astop in the direction opposite of the wind-up if the belt breaks. If thebelt breaks, the notch 27 would stop the first tensioner component 5once it moved back down the ramp and would keep the first tensionercomponent 5 from moving up the adjacent ramp up in the directionopposite of the wind-up.

Referring now to FIG. 4, the upper ramp surface 7 of the ramp bushing 3has ramp features arranged in a substantially circular array around thepivot axis 11. The ramp features 6 of the second tensioner component 4,the tensioner component 5, and the lower ramp surface 8 of the rampbushing 3 may also be arranged similarly. The upper ramp surface 7 andramp features 9 of the tensioner component 5 are designed to be incontact during normal operation of the tensioner 10. Likewise, the lowerramp surface 8 and the ramp features 6 of the second tensioner component4 are designed to be in contact during normal operation of the tensioner10. The ramp features depicted in FIG. 4 show a substantially symmetricpattern whereby each discrete repeating ramp element has substantiallythe same pattern up and down. The ramp features may vary in the radialdirection from the pivot axis in order to maintain a constant interfacewith the mating surface and modulate specific properties of the damperduring operation. Although the upper ramp surface 7 of the ramp bushing3 shows a symmetrical repeating pattern, the ramp features can have aunique or alternatively an asymmetric pattern to achieve specificoperational characteristics. The general structure of an arbitrarysection of ramp features on both the upper and lower ramp surfaces 7, 8of the ramp bushing 3, the second tensioner component 4, and thetensioner component 5 can be broken into four repeating elements. Theseelements are lower dwell 30, ramp-up 32, upper dwell 31, and ramp-down33, as shown in FIG. 4.

A schematic detail view of the ramp bushing 3 positioned between thefirst tensioner component 5 and the second tensioner component 4 isshown in FIG. 5A as contact region 34. The lower dwell 30, ramp-up 32,upper dwell 31, and ramp-down 33 are shown for the second tensionercomponent 4 in FIG. 5B and for the ramp bushing in FIG. 5C. Although thecontact region 34 shown in FIG. 5A details a set of straight-linefeatures, two important points must be recognized. First, in the radialdirection away from the axis of rotation of the device, the actual rampprofiles may vary significantly along this reference line in order tominimize relative slipping, reduce friction, provide balanced loading,and achieve other objectives. An example of one embodiment of thisapproach can be seen in the isometric profile shown in FIG. 4 where thesame lower dwell 30, ramp-up 32, upper dwell 31, and ramp-down 33surface features are depicted. Second, although the profiles shown inFIGS. 5A-5C are straight lines, the device can use any number ofalternative profiles for the ramps including multi-faceted orcurvilinear forms. For example, the upper and lower dwells 31 and 30respectively could be merely fillets or radius connecting the upward anddownward ramps, similar to the embodiment shown in FIG. 4.

Alternatively the dwells 30, 31 and ramps 32, 33 could be constructed insuch a way as to provide a detent or delay in switching between normaloperation and the asymmetric damping needed during a wind-up situation.The shape of the ramp features (up and down and dwells) may be selectedfrom a wide variety of profiles with a wide range of rectilinear andcurvilinear shapes. The ramp features may be repeated at any arbitraryinterval over the length of the ramp feature or be unique with norepeating pattern whatsoever. Although the embodiment depicted here hasa symmetric repeating profile, where each edge of a specific rampfeature has equivalent features on each side, it is also possible to usean asymmetric profile. The asymmetric profile can at the extremeresemble a saw-tooth configuration, where the areas of the ramp featuresnot in contact are typified by a sharp drop rather then a gradualramp-down. The number of ramp features, as defined as a single unit maybe selected from a wide range of possible alternative arrangements.Preferably the number of ramp feature units is equal to or more thanfour. More preferably the number of ramp features is equal to or morethan six. Most preferably the number of ramp features is equal to orgreater than eight.

Referring to FIGS. 5A-5C, a contact region 34 is shown between the endcap 4 having ramp features 6 and the first tensioner component 5 havingramp features 9. The contact region 34, as shown, also includes a rampbushing 3 having an upper ramp surface 7 and a lower ramp surface 8positioned between the first tensioner component 5 and the end cap 4.FIG. 5A shows the first tensioner component 5 seated in a down-rampposition 36. During a wind-up condition (i.e., the tensioner arm ismoving away from the belt), the rotation of the tensioner arm provides atorsional force that can move the tensioner components 4, 5 relative toone another such that one component moves up the ramp-up 32 of theother. The movement of a component up a ramp creates a normal force thatmoves a component of the tensioner 10 against the arm 1 to applyfrictional damping to the arm 1 such that the arm 1 can resist beingmoved away from the belt. FIG. 5B shows the first tensioner component 5and the ramp bushing 3 having moved rotatably in response to a torsionalforce (F_(T)) where F_(T) is equal to the friction torque applied fromthe damper bushing 18 by the rotation of the tensioner arm 1 into anup-ramp position 38. Alternately, as shown in FIG. 5C the firsttensioner component 5 may move rotatably in response to a torsionalforce (F_(T)) applied by the rotation of the tensioner arm into anup-ramp position 39 while the ramp bushing 3 remains seated against theramp features 6 of the end cap 4. Then from either of the up-ramppositions 38 or 39 the first tensioner component 5 may move back to thedown-ramp position once the torsional force (F_(T)) dissipates enough toallow the spring torque to move the first component down ramp-up 32.

When the first tensioner component 5 is in either of the up-ramppositions 38 or 39 there is a translational movement of the firsttensioner component 5 relative to the pivot axis, which will increasethe normal force applied against the tensioner arm 1 for frictionaldamping by pressing the first tensioner component 5 itself or a damperbushing 18 coupled to the first tensioner component 5 against thetensioner arm 1. When the wind-up condition dissipates the torque on thearm 1 is reduced and the arm 1 no longer moves away from the belt. Thetorsional spring 2 can now apply a force to the arm to move the arm intothe belt and back toward its normal operating condition thereagainst. Asthe arm moves back toward its normal operating condition, the torque onthe torsional spring 2 is reduced which reduces the torque on the firsttensioner component 5 such that the first tensioner component 5 willmove back down the ramp-up 32 to a down-ramp position 36, as shown inFIG. 5A, to restore the torsional spring 2 to its pre-wind up state.When the first tensioner component 5 moves down the ramp up, the normalforce is reduced and ultimately the frictional force on the arm 1 isreduced and achieves the desired asymmetric damping.

The magnitude of tension provided by the tensioner arm 1 against thebelt during normal operation is predominantly controlled by thetorsional spring 2 which is dictated by the amount of pre-loading,spring constant, and other well-controlled characteristics of torsionalsprings know to those of ordinary skill in the art. The spring constantof the torsional spring 2 is controlled in order to create therotational force experienced by the first tensioner component 5 duringboth normal operation and during the wind-up condition. The use of aflatwire spring 2 in the tensioner 10, as shown in FIG. 1, isadvantageous because the flatwire spring has a lower torque per degreeof rotation and less degrees of variation than a round wire spring. Aflatwire spring also has less resonance issues than a round wire springand the use of spring tape between the spring's coils can further reducenoise. Additionally, the flatwire spring reduces the tensioner's 10axial height (H) for the clutch assembly 25, FIG. 2, (minimally thesecond tensioner component 4, first tensioner component 5, the torsionalspring 2, and the damper bushing 18 and optionally including the rampbushing 3 and pivot bushing 15), which can be advantageous in installingthe tensioner in various motor configurations. While the flatwire springprovides reduced axial height (H), the width (W) of the clutch assemblymay be increased, which actually provides an advantage in that thedamper bushing which applies the frictional damping against the arm willhave a larger surface area allowing for decreased pressure against thearm to produce the friction force resulting in less wear on the arm andthe damper bushing and reduced change of the arm and damper bushing“locking” up.

The operation of the tensioner 10 and the rate or profile of asymmetricdamping can be modulated by controlling several features of thetensioner using techniques known to those of ordinary skill in the art.The upper and lower ramp surfaces 7, 8 of the ramp bushing 3, the rampfeatures 9 of the tensioner component 5, and/or the ramp features 6 ofthe second tensioner component 4 may be modulated to vary the amount offrictional force generated due to application of a specific normalforce. These components may be modulated by changing the characteristicsof the ramp features, such as the profile, size, number, structure, andrelative friction thereof, on at least one of the components having rampfeatures. The ramp features can have a variety of different profiles andshapes in order to modify the operation of the device and translate therotational movement of the first tensioner component 5 into an axialmovement of the damper bushing 18 into the tensioner arm 1.Additionally, the frictional properties of the interface between theramp bushing 3 and the first tensioner component 5 and the secondtensioner component 4 may be modulated. There are a number of differentmethods for adjusting the friction properties of surfaces includingspecific surface treatments and finishes, structures, and even materialselection.

The ramp features may be coated or otherwise treated in order tominimize the ramp feature to ramp feature interface friction. Specificmethods of achieving this goal can include coating the surface with anumber of different materials including metallic, ceramic, and orplastic materials, including, but not limited to brass, aluminum, oilimpregnated bronze, silicon nitride, Teflon®(polytetrafluoroethylene—PTFE), ultra high molecular weight polyethylene(UHMWP), or high density polyethylene. These materials may either formthe entire ramp feature as one unit or be applied to a substrate orstructural materials in order to achieve specific load bearing andfriction characteristics.

FIGS. 6 and 7A-7B depict another embodiment of a tensioner, generallydesignated 100, with asymmetric damping that may be adapted to supportan idler pulley 22 shown in FIG. 1. The tensioner 100 includes atensioner arm 102 that defines a cup 104 and an arm arbor 106 and ispivotable about a pivot axis 111, a spring case 140 having a spring casearbor 141 for connecting the spring case 140 to the arm 102, and a mainspring 142 between the arm 102 and the spring case 140 such that thespring case houses the main spring. The main spring may be a torsionalspring such as a coil spring, roundwire spring, a flatwire spring, orany other type of spring known to one of skill in the art to providespring torque to the arm 102 to tension a belt. The main spring 142 mayhave a first and a second spring tang. The first spring tang may connectthe main spring 142 to the arm arbor 106 and the second tang mayconnection the main spring 142 to the spring case 140. These connectionsmay be similar to the connections shown in FIGS. 7A and 7B for thedamper spring 114 or any other connection known to one of skill in theart. The tensioner 100 may also include a pivot bushing 144 that fitsbetween the arm arbor 106 and the spring case arbor 141 and a springbushing 146 positioned where the outer edge of the spring case 140 meetsthe arm 102 to reduce friction therebetween and facilitate the rotationof the arm relative to the spring case.

The tensioner 100 also includes a ramp-ramp assembly 101 that may bereceived in the cup 104. The cup 104 of the arm 102 may be recessed intothe arm enough to accept at least part of the ramp-ramp assembly 101 andis shaped and sized so the ramp-ramp assembly 101 is freely rotatablewithin the cup 104 and about the tensioner axle 108. The ramp-rampassembly 101 may include a damper bushing 110, a ramp hub 112, a damperspring 114, a ramp bushing 116, and an end cap 118.

The damper bushing 110 may be substantially an outward flared cone shapewith an at least partially flat bottom that includes one or more tabs128, shown in FIG. 7A, for mating the damper bushing 110 to the ramp hub112. The ramp hub 112 may likewise have substantially outward flaredcone shaped sides or a substantially cylindrical shaped sides that allowthe ramp hub 112 to fit within the cone shape of the damper bushing 110.The ramp hub 112 may include hub ramp features 113, a first tangreceptor 124, and one or more notches 130 spaced to receive the one ormore tabs 128 of the damper bushing 110. The hub ramp features 113 maybe similar to those described above in detail. One of skill in the artwill appreciate that numerous ways of mating the damper bushing 110 tothe ramp hub 112 are known besides a tab and notch arrangement. Theexterior of the damper bushing 110 may form a friction interface withthe inside of the cup 104 of the tensioner arm 102. The damper bushing110 and the cup 104 can adopt a number of different forms including, asshown, a cup and cone shape or alternately a more cylindrical shape,ball and socket shape, or the like. The friction interface between thedamper bushing 110 and the cup 104 rotatably links the movement of theramp hub 112 through its connection to the damper bushing 110 to therotation of the tensioner arm 102 such that rotation of the arm rotatesthe ramp hub 112 in the same direction about the pivot axis 111.

The ramp hub 112 may be adapted to receive the damper spring 114 thereinand as such acts as a damper spring case. The damper spring 114 may be atorsional spring such as a coil spring, roundwire spring, a flatwirespring, or any other type of torsional spring known to one of skill inthe art. The damper spring 114 may have a first tang 120 and a secondtang 122. The first tang 120 may be received in a first tang receptor124 of the ramp hub 112. The second tang 122 may be received in a secondtang receptor 126 located in the end cap 118. The end cap 118 may alsoinclude end cap ramp features 119 for mating with the hub ramp features113. The end cap ramp features 119 may be similar to those described indetail above.

The ramp-ramp assembly 101 may include a ramp bushing 116. The rampbushing 116 may have a hub side having a hub ramp surface 132 and a capside having a cap ramp surface 134. The ramp bushing 116 may be disposedbetween the ramp hub 112 and the end cap 118 and may be in directcontact therewith. When the ramp bushing 116 is so disposed, the hubramp surface 132 mates with the hub ramp features 113 and the cap rampsurface 134 mates with the cap ramp features 119. The ramp bushing 116may be both rotatable about and translatable up and down the pivot axis111.

The end cap 118 may be substantially fixed to the tensioner axle 108such that it does not substantially translate or rotate along or aboutthe pivot axis 111. The end cap 119 may be fastened to the spring casearbor 141 such as by riveting, welding, bolting, adhering, or otherfastening techniques known to one of skill in the art as explainedabove.

During normal tensioning, when a belt presses against a pulley attachedto the tensioner arm 102, the arm will rotate about the pivot axis 111thereby winding the main torsional spring 142. The main torsional spring142 upon winding will apply spring torque against the arm 102 to move,hold, or press the arm and pulley against the belt. When the arm 102rotates about the pivot axis 111 winding the main torsional spring 142,the frictional contact between the arm 102 and the damper bushing 110causes the damper bushing and the ramp hub 112 connected thereto torotate, which un-winds the damper spring 114. The wound damper spring114 provides spring torque against the ramp hub 112 and damper bushing110 urging the ramp hub 112 in the opposite direction as the main spring142 thereby increasing damping, or arm resistance in one directionagainst the belt.

During belt tensioning when no rotation of the tensioner arm hasoccurred the ramp features of the ramp hub 112, of the ramp bushing 116,and of the end cap 118 are seated in a down-ramp position relative toone another so the distance between the ramp hub 112 and the end cap 118is minimized and likewise the frictional damping between the damperbushing 110 and the tensioner arm 102 is minimized because the damperbushing 110 is not pushing against the tensioner arm 102 with as muchforce (i.e., the Normal force applied to the arm is reduced).

When the tensioner arm 102 is pushed away from the belt (wind-up), themovement of the tensioner arm 102 rotates the damper bushing 110 and theramp hub 112 and unwinds the damper spring 114. The rotation of the ramphub 112 causes the ramp hub's ramp features 113 to move up the hub rampsurface 132 of the ramp bushing 116 or to move with the ramp bushing 116up the ramp features 119 of the end cap 118. This may be called anup-ramp position. The movement of the ramp hub 112 up the ramp moves theramp hub 112 and the damper bushing 110 translationally in relation tothe pivot axis 111 and maximizes the distance between the ramp hub 112and the end cap 118. The translational movement of the ramp hub 112pushes the damper bushing 110 against the tensioner arm 102 (i.e.,increasing the Normal force) for frictional damping. The movement of theramp hub 112 up the ramp is partially dictated by the severity of thewind-up condition, the configuration of the ramp features 113 and 119and the hub ramp surface 132 and the cap ramp surface 134, and thecharacteristics of the torsional spring 114. The characteristics ofthese components may be pre-selected to achieve desired asymmetricdamping profiles relative to the wind-up conditions encountered, i.e.the profile and characteristics of the ramp features 113, 119 and of thehub and cap ramp surfaces 132, 134 of the ramp bushing 116, and thefriction interfaces between the various components, using techniques asdescribed above.

After the wind-up condition dissipates the torque, the damper spring 114provides a spring torque to the damper bushing 110 and ramp hub 112 thatmoves the ramp hub 112 relative to the end cap 118 back into thedown-ramp position. When the ramp hub 112 moves down the ramp thedistance between the ramp hub 112 and the end cap 118 is again minimizedor reduced. This movement reduces the force pressing the damper bushing110 against the tensioner arm 102, which reduces the normal forceapplied to the friction interface therebetween to reduce the frictionaldamping. This second embodiment will have the same advantages as thefirst embodiment in relation to using a ramp bushing and a flatwirespring as shown in FIGS. 6 and 7A-7B.

The embodiments of this invention shown in the drawing and describedabove are exemplary of numerous embodiments that may be made within thescope of the appended claims. It is contemplated that numerous otherconfigurations of the tensioner assemblies may be created takingadvantage of the disclosed approach. In short, it is the applicant'sintention that the scope of the patent issuing herefrom will be limitedonly by the scope of the appended claims.

What is claimed is:
 1. A tensioner comprising: a tensioner axle defining a pivot axis; an arm mounted on the tensioner axle so as to permit the arm to pivot about the pivot axis; a first tensioner component having at least one first ramp features, the first tensioner component engaged to the arm for rotation therewith and being translatable along the pivot axis; a second tensioner component having at least one second ramp features, the second tensioner component coupled to the tensioner axle; and a ramp bushing having an upper ramp surface and a lower ramp surface, the ramp bushing being disposed between the first tensioner component and the second tensioner component such that the upper ramp surface seats within the first ramp features and the lower ramp surface seats within the second ramp features.
 2. The tensioner of claim 1 wherein the ramp bushing is translatable along the pivot axis and rotatable about the pivot axis.
 3. The tensioner of claim 1 further comprising a torsional spring that has an inner tang and an outer tang, wherein the outer tang is coupled to the first tensioner component and the inner tang is coupled to the arm.
 4. The tensioner of claim 3 wherein the torsional spring is a flatwire spring.
 5. The tensioner of claim 3, wherein when the arm pivots in a first direction the first tensioner component rotates with the arm relative to the second tensioner component to urge the first ramp features to slide along either the upper ramp surface of the ramp bushing or along the second ramp feature of the second tensioner component which causes translation of the first tensioner component toward the arm for increased frictional engagement therewith to dampen the movement of the arm.
 6. The tensioner of claim 1, wherein the first and the second ramp features and the upper and lower ramp surfaces have geometries pre-selected to provide a desired change in frictional damping in response to the arm pivoting about the pivot axis.
 7. The tensioner of claim 1, wherein the first and the second ramp features and the upper and the lower ramp surfaces are comprised of a plurality of ramp-ups and ramp-downs in a generally circumferential array about the pivot axis.
 8. The tensioner of claim 1, wherein the first tensioner component is positioned between the arm and the second tensioner component.
 9. The tensioner of claim 8, wherein the second tensioner component is an end cap for the tensioner.
 10. The tensioner of claim 1 further comprising a damper bushing coupled to the first tensioner component, the damper bushing positioned for frictional contact with the arm.
 11. The tensioner of claim 1 further comprising a spring having a first tang and a second tang, wherein the first tang is coupled to the first tensioner component and the second tang is coupled to the arm.
 12. A tensioner comprising: a tensioner axle defining a pivot axis; an arm mounted on the tensioner axle so as to permit the arm to pivot about the pivot axis; and a clutch assembly mounted at least partially to the tensioner axle and coupled to the arm, the clutch assembly comprising: a first tensioner component having first ramp features, the first tensioner component engaged to the arm for rotation therewith and being translatable along the pivot axis; a second tensioner component having second ramp features, the second tensioner component coupled to the tensioner axle; a flatwire spring having a first end and a second end, wherein the first end is coupled to the first tensioner component; and a damper bushing coupled to the first tensioner component, the damper bushing positioned for frictional contact with the arm.
 13. The tensioner of claim 12 further comprising a ramp bushing having an upper ramp surface and a lower ramp surface, the ramp bushing being disposed between the first tensioner component and the second tensioner component such that the upper ramp surface seats within the first ramp features and the lower ramp surface seats within the second ramp features.
 14. The tensioner of claim 12 wherein the second end of the flatwire spring is coupled to the arm and the first tensioner component pivots about the pivot axis with the arm in a first direction relative to the second tensioner component to urge the first ramp features of the first tensioner component to slide along the second ramp features of the second tensioner component which causes translation of the first tensioner component toward the arm for increased frictional engagement therewith.
 15. A tensioner comprising: a tensioner axle defining a pivot axis; an arm mounted on the tensioner axle so as to permit the arm to pivot about the pivot axis; a first tensioner component having first ramp features, the first tensioner component engaged to the arm for rotation therewith, translatable along the pivot axis, and defining a spring case; a second tensioner component having second ramp features, the second tensioner component coupled to the tensioner axle; a spring seated in the spring case defined by the first tensioner component. 